1. Field of the Invention
The present invention relates to a self-priming pumping system. More particularly, the present invention relates to self-priming pumping systems of the type described in U.S. Pat. Nos. 3,370,604 and 3,381,618, the contents of which are incorporated herein by reference.
2. Description of the Prior Art
In the past, there have been many different devices developed to automatically prime a liquid pump when the pump runs dry due to an insufficient amount of liquid being present at the pump inlet and to prevent air from being introduced to the suction side of the pump. These devices are essential to the efficient operation of a pumping system, since, as is well known, once air is admitted to the suction passage in sufficient quantities to allow the pump to exhaust the supply of liquid in the suction well, the pump no longer is able to maintain suction to pump the liquid. Consequently, the pumping operation must be stopped and the attention of an operator is required, if no automatic mechanism for repriming the system is provided.
Previously known automatic mechanisms, such as those described in the aforementioned U.S. patents and U.S. Pat. No. 3,434,430, generally provide satisfactory performance; however, problems are sometimes encountered when pumping high viscosity liquids over prolonged periods of time. During such pumping operations, vapor pressures can build up within the system and cause unnecessary actuations of the self-priming system. Also, difficulty has been experienced with previously known self-priming systems when the systems are used to pump liquids having different viscosities and/or vapor pressures.